LONDON — The London Underground is starting its first-ever overnight service, a move city leaders hope will make the British capital a truly 24-hour city and bolster the local economy.

The new service will only run on weekends and initially be available on just two of the most-well-travelled lines. But the initiative reflects London’s growing population and cosmopolitan mentality, marking a coming of age for a city that many in the Big Apple regard as quaint and sleepy.

“It’s a psychological step because metros and subways and the Underground are always such totemic parts of cites,” Tony Travers, an expert on urban issues at the London School of Economics, said. “They are like the circulation system of a city.”

Economists like to point out that London is already a 24-hour city, with West End theatres, Michelin-starred restaurants and trendy nightclubs attracting customers from around the world well into the wee hours.

But the expanded Tube service comes at a good time for London, which has been anxious to reassure the world that the city is open for business and ready to welcome tourists despite Britain’s recent vote to leave the European Union.

Efforts to keep the city humming around the clock have already produced 40 billion pounds ($52 billion) of economic benefits for the city, and the Night Tube service could be worth another 77 million pounds ($100 million), according to the business group London First.

“At a time of economic uncertainty — particularly following the Brexit vote — this is a welcome boost to London’s economy,” London First said in a statement.